1. Field of the Invention
The present invention relates to a pump with a pulsation suppression device, and more particularly to a pump with a pulsation suppression device which is preferably applied to, for example, circulating transportation of chemical liquids used in various processes such as surface washing on ICs in a semiconductor producing device or a liquid crystal display device.
2. Description of the Prior Art
As a pump with a pulsation suppression device of this kind, the assignee of the present invention has already proposed a configuration which is disclosed in, for example, Japanese Patent Publication Laying-Open No. 10-196521. In the proposed configuration, a pump head wall has inflow and out-flow passages for liquid, and an air-driven reciprocal pump portion and a pulsation suppressing portion are integrally disposed respectively on the sides of the pump head wall, so as to be opposed to each other.
The air-driven reciprocal pump portion comprises: a first bellows which is extendable and contractible in the axial direction in a casing that is disposed in one side portion of the pump head wall; an air cylinder portion which drives the first bellows so as to extend and contract; and a pump working chamber in which check valves are disposed inside the first bellows. The check valves are alternately opened and closed in accordance with the extending and contracting operations of the first bellows to suck and discharge the liquid.
On the other hand, the pulsation suppressing portion comprises: a second bellows which is disposed in a casing that is disposed in the other side portion of the pump head wall, so as to be extendable and contractible; a liquid chamber which is formed inside the second bellows, and which can temporarily store the liquid that is to be discharged from the pump working chamber via the discharge check valve; and an air chamber which is formed outside the second bellows so as to be isolated from the liquid chamber, and which is to be filled with air for suppressing pulsation. Pulsation due to the discharge pressure of the liquid which is discharged from the pump working chamber is reduced by a change in the capacity of the liquid chamber due to extension and contraction of the second bellows.
In a pump of this kind, the pump performs the pulsation suppression in the following manner. When the transported liquid discharged from the reciprocal pump portion and having a high pressure is to be received by the second bellows, the transported liquid is caused to flow into the liquid chamber of the second bellows while extending the second bellows, thereby absorbing the high pressure of the transported liquid. The transported liquid is temporarily stored in the liquid chamber of the second bellows, and then discharged from the out-flow passage while reducing the pressure of the transported liquid. In this case, the extending operation of the second bellows depends on the balance between the pressure of the transported liquid flowing into the liquid chamber of the second bellows, and the pressure of the air chamber which functions against the transported liquid pressure via the second bellows. Usually, a buffering function of a higher degree is obtained as the second bellows can extend more freely in accordance with the transported liquid pressure, and without being affected by the pressure rise of the air chamber due to the contraction of the air chamber corresponding to the extension displacement of the second bellows.
In the pump with a pulsation suppression device, the first bellows is formed by a fluororesin such as polytetra-fluoroethylene which has excellent heat and chemical resistances so as to comply with circulating transportation of chemical liquids used in a semiconductor producing device or the like. Also the second bellows is formed by the same resin material as that described above, and has the same thickness as the first bellows so that the extension rates of the first and second bellows are strictly identical with each other. Therefore, the second bellows tends to extend and contract with laggingly following variation of the discharge pressure from the pump portion. In other words, the response property of the second bellows with respect to a pulsative pressure is low. As a result, the effect of suppressing pulsation cannot be sufficiently attained.
The present invention has been conducted in order to solve the problem.
It is an object of the invention to provide a pump with a pulsation suppression device which can further enhance the effect of suppressing pulsation.
The pump with a pulsation suppression device of the invention will be described with reference to the accompanying drawings. The reference numerals in the figures are used in this paragraph in order to facilitate the understanding of the invention, and the use of the reference numerals is not intended to restrict the contents of the invention to the illustrated embodiments.
The pump with a pulsation suppression device of the invention comprises: a pump head wall 1 having inflow and out-flow passages 2 and 3 for liquid; an air-driven reciprocal pump portion 4 comprising: a first bellows 7 which is made of a resin, and which is extendable and contractible in an axial direction in a casing 6 that is disposed in one side portion of the pump head wall 1; an air cylinder portion 14 which drives the first bellows 7 so as to extend and contract; and a pump working chamber 9a in which a check valve 16a for sucking and a check valve 16b for discharging are disposed inside the first bellows 7, the check valves being alternately opened and closed in accordance with the extending and contracting operations of the first bellows to suck and discharge the liquid; and a pulsation suppressing portion 5 comprising: a By second bellows 18 which is made of a resin, which is disposed in a casing 17 that is disposed in another side portion of the pump head wall 1, and which is extendable and contractible; a liquid chamber 20a which is formed inside the second bellows 18, and which can temporarily store the liquid that is to be discharged from the pump working chamber 9a via the discharge check valve 16b; and an air chamber 20b which is formed outside the second bellows 18 to be isolated from the liquid chamber 20a, and which is to be filled with air for suppressing pulsation, the pulsation suppressing portion causing pulsation due to a discharge pressure of the liquid which is discharged from the pump working chamber 9a, to be absorbed by a change in a capacity of the liquid chamber 20a due to the extending and contracting operations of the second bellows 18, and is characterized in that an extension rate of the second bellows 18 is set to be larger than an extension rate of the first bellows 7.
In this specification, the extension rate means the extension rate of an extending and contracting portion of each of the first and second bellows in the case where a pressure of a certain level is applied to the interior of the first or second bellow.
In the invention, the first and second bellows may be formed by a same resin material, and a thickness of the second bellows may be smaller than a thickness of the first bellows. In this case, preferably, the thickness ratio (second bellows/first bellows) of the first and second bellows is smaller than 1. As the same resin material of the first and second bellows, it is desirable to use polytetrafluoroethylene which has excellent heat and chemical resistances.
According to the thus configured pump with a pulsation suppression device of the invention, when the first bellows of the reciprocal pump portion is driven via the air cylinder portion so as to extend and contract, the suction and discharge check valves in the pump working chamber are alternately opened and closed, so that suction of the liquid from the liquid inflow passage into the pump working chamber, and discharge of the liquid from the pump working chamber into the liquid out-flow passage are repeated to conduct a predetermined pumping action. At this time, the liquid which is discharged from the pump working chamber via the discharge check valve flows out through the liquid chamber of the pulsation suppression portion into the out-flow passage. In this case, in a peak portion of the pulsation of the discharge pressure of the discharged liquid, the second bellows moves in the direction along which the capacity of the liquid chamber is increased, thereby absorbing the pressure, and, in a valley portion of the pulsation, the second bellows moves in the direction along which the capacity of the liquid chamber is reduced, so that the pressure of the discharged liquid is raised to absorb the pulsation. As a result, the liquid can be caused to flow out continuously and smoothly with a reduced degree of pulsation.
When the extension rate of the second bellows is set to be larger than the extension rate of the first bellows, particularly, the response property of the second bellows with respect to the pulsative pressure is remarkably improved, and therefore the effect of suppressing pulsation can be further enhanced.